The present invention relates to a header structure of a heat exchanger for radiators, condensers and the like.
As a header structure of a conventional heat exchanger, there is for example, a structure described in Japanese Patent Laid-open No. 105400-1988. This header structure is characterized by a tank member having a transverse cross-section formed in a circular arc shape and a flat tube attachment member. The tank member and plate member are joined by brazing.
In addition, there is a header structure described in Journal of Nippondenso Technical Disclosure No. 69-154 (issued on Jan. 15, 1990). In the header structure, a tank member having a transverse cross-section of a circular arc shape and a tube attachment member having a transverse cross-section of a circular arc shape are combined to constitute a cylindrical header. A brazing material is poured into an inner peripheral face of a joining portion between the tank member and the tube attachment member in order to have a smooth finish. The concentration of stress at the joining place is prevented by making smooth the inner peripheral face of the joining portion.
However, there is a problem that either one of the above-mentioned former and latter header structures is not well suited to be used as a condenser or a radiator of the condensation type for which high pressure resistance is required. For example, in the former header structure, not only is the tube attachment member flat and has poor pressure resistance, but the stress is concentrated at the joining portion which is bent at an acute angle between the tank member and the tube attachment member. Therefore, no sufficient pressure resistance is obtained with the above-mentioned applications by the former header structure.
On the other hand, since the header is constructed in a cylindrical shape in the latter header structure, pressure resistance which is basically higher than that of the former is obtained; however, production is difficult due to the fact that the brazing material is poured into the inner peripheral face of the joining portion to make the inner peripheral face smooth, and there is the possibility that the brazing material is not supplied sufficiently and brazing deficiency may take place. If brazing is deficient, the strength is lowered and the cylindrical header must be formed in a larger size.